Many irrigation systems have been developed that automatically control the application of water to landscapes. These irrigation systems can range from simple systems that vary irrigation on a timed control basis, to very complex systems that vary irrigation based on climatic, geographic, and seasonal conditions. The complex systems can rely on various sources for data, including sensors and other devices that generate data locally, as well as governmental or commercial providers of information.
The watering intensity applied to a lawn, garden, farm, or any other application can be thought of as involving two components: (1) the cycle amount applied during a given application; and (2) the frequency of the application cycle. If, for example, a homeowner applies 0.3 inches of water to his lawn, twice a week, then the cycle amount of water is 0.3 inches, and the frequency is twice a week.
Relatively simplistic irrigation systems require manual changing of both the cycle amount and the frequency (See FIG. 1, item 1). For example, in the late Spring, a user having a standard irrigation system as in item 1 generally needs to increase both cycle amount and frequency relative to the Winter months. The user may make one or more additional increases during the Summer, and then decrease cycle amount and frequency during the Fall when it becomes cooler and the vegetation does not require so much watering. Unfortunately, these relatively infrequent seasonal modifications are typically insufficient to achieve efficient watering.
More complex controllers are known that make relatively frequent automatic compensations for environmental conditions. Exemplary systems that use evapotranspiration data (ETo data), for example, are discussed in U.S. Pat. No. 5,479,339 issued December, 1995, to Miller, U.S. Pat. No. 5,097,861 issued March 1992 to Hopkins, et al., U.S. Pat. No. 4,176,395 issued November 1979 and U.S. Pat. No. 5,229,937 issued July 1993 both to Evelyn-Veere, U.S. Pat. No. 5,208,855, issued May 1993, to Marian, and U.S. Pat. No. 5,696,671, issued December 1997, and U.S. Pat. No. 5,870,302, issued February 1999, both to Oliver. Other systems utilize temperature or soil moisture sensors.
Regardless of the mechanism(s) used to determine changes in environmental conditions, however, each of the known systems except U.S. Pat. Nos. 5,696,671 and 5,870,302 is directed to replacement of moisture lost due to evapotranspiration between the currently scheduled watering and the last previous watering. Thus, if the irrigation system is set to water daily, and the evapotranspiration on the previous Summer day was 0.25 inches, then the following day the irrigation system would apply 0.25 inches of water. If the system were set for every other day watering, then the next watering would apply 0.50 inches of water.
Items 2, 3, 4, and 5 of FIG. 1 summarize prior art irrigation systems in which the watering schedule and/or amount are partly derived from ETo data, such that the amount applied is that estimated to have been lost due to evapotranspiration. Even so, the irrigation frequency is similar to a standard irrigation system in that a day schedule is manually entered, and the irrigation applications are executed on one or more of those days (e.g., Mon-Wed-Fri, or Tue-Thu). The automatic features are that (a) rain days can automatically be skipped through use of a rain sensor, (b) the cycle amount varies according to the accumulated evapotranspiration loss, and (c) the irrigation applications may be split into two or more watering intervals to avoid excessive runoff.
It is not, however, always advantageous to apply the amount estimated to have been lost to evapotranspiration. For example, if the systems described above were to operate in late Fall when the evapotranspiration is perhaps only 0.06 inches per day, the system would try to apply only 0.06 inches on a daily watering schedule. Applying such an amount would be entirely impractical, and even if it could be accomplished, such shallow watering is bad for most crops. In the past, the shallow watering problem has usually been resolved by manually reducing the frequency by limiting the day schedule. For example, instead of watering 0.06 inches seven days a week, the schedule could be limited to one day a week, which would provide 0.42 inches of water on that one day. Such modifications to the day schedule can provide sufficiently deep watering, but is only effective where the user makes the required modifications.
Problems arise, for example, when a user fails to sufficiently alter the day schedule to accommodate weather changes. Such failure could occur because of user neglect or lack of training, because of extraordinarily hot or cold weather, or for other reasons. Whatever the reason, the known systems except U.S. Pat. Nos. 5,696,671 and 5,870,302 operate during such periods by watering excessively small amounts too frequently, or excessively large amounts too infrequently. Both conditions can cause serious damage to grass or other crops, or at least result in significantly suboptimal growth.
U.S. Pat. No. 5,870,302, summarized as item 6 of FIG. 1, addresses these problems by automatically varying the irrigation watering frequency. There, soil moisture is detected or estimated, and irrigation is commenced at the next available scheduled time slot whenever the moisture level is deemed to Fall below a threshold deficiency level. The cycle amount is calculated as being that amount of water necessary to raise the soil moisture back up to full field capacity
Unfortunately, determinations of the threshold deficiency level and the cycle amount can be exceedingly complex. The threshold deficiency level, for example, is based on several factors including ETo, and is necessarily specific for each irrigated site. The cycle amount is also based upon several factors, including ETo, sensor data, and possibly forecasted weather data. The complexity of these calculations is such that once the irrigation deficiency and full field capacity levels are determined for a site, they are fixed, and future irrigation applications are based on those fixed values. Thus, devices and methods according to the '302 patent have limited applicability, and are mostly suitable for large irrigated sites, or situations in which a central computer is used to control multiple irrigation sites.
Thus, there is still a need for systems and methods that automatically execute irrigation applications to achieve deep watering at an irrigated site, that vary the deep watering parameters to meet seasonal changes, environmental changes, crop maturity changes and other yearly changes to optimize the efficient irrigation of the plants, and that can be used cost effectively to irrigate residential and small commercial sites.